The average distance between molecules always increases during which of the following phase changes?

A. gas to solid

B. liquid to gas

C. gas to liquid

D. liquid to solid

B. liquid to gas

Explanation:

Matter exists in 3 different states:

- Solid: in solids, particles in the substance are tightly bond to each other through strong intermolecular forces. Therefore, they can only vibrate around their fixed position, but they cannot move freely: as a result, the distance between the particles is the smallest among the 3 states of matter.

- Liquid: in a liquid, particles are able to slide past each other, however there are still intermolecular forces keeping them not too far from each other. As a result, in liquids, particles are on average more distance from each other compared to solids.

- Gas: in a gas, particles are completely free to move, as the intermolecular forces between them are negligible. As a result, in gases, the distance between molecules is the greatest, compared with solids and liquids.

Therefore, the phase changes in which the average distance between molecules increases is:

B. liquid to gas